I'm finally going through this big pile of stuff I got with my Crown Graphic 4x5, and along with the 3 cell Heiland flash (7" reflector) are two flashbulb adapters.

One adapter obviously fits the Press 25 bulb (as I have some that came with the camera) - a bayonet type adapter about 1/2 inch in diameter.

The other adapter I have no idea. It has the large screw base to fit into the Heiland synchronizer, and then it "adapts" to a screw base which appears to be about 3/8" in diameter. What sort of bulb is this for?